Repeater switching telephone system



March 14, 1950 J. wlcKS REPEATER SWITCHING TELEPHONE SYSTEM 6 Sheets-Sheet 2 Filed March 25, 1948 m8 v Q l l 8 mm :cOU :OH MIN fiw 00m $8 mom owm @m @5585 wow wow

INVENTOR.

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81H 0 Now r J k 43% mwm ,olz alq ouoo March 14, 1950 J. WICKS REPEATER SWITCHING TELEPHONE SYSTEM Filed March 25, 1948 6 Sheets-Sheet 4 3; m N E o? m 83 a3 88 228 mm :58 2 8 85 omvm Q3 52?? 6 R p J. q II ll? 3i mm 3 .o\.| mm P 5 s w m? w wwv M80 mwvm ilmmo mwo WQZL T v? John Wicks Attys.

?aientecl Mar. 14, 1950 ENT OFFICE REPEATER SWITCHING repet tions SYSTEM John Wicks, Biloxi, Miss, assignor to Automatic Electric Laboratories, Inc Chicago, 111., a corporation of Delaware Application March 25, l dflgflerialhlo. 16,905

12 Claims. 1

Thepresent-invention relates to automatic telephone systems, and more particularly to such sys- *'items .iincorporating repeater switching arrangements. p

'iIt is .a general object 50f the present .invention to providein'an automatic telephone system an "improved repeater switching arrangement in :whitih digits are 3transmitted from a calling switchboard tothe automatic switches via a special control conductor independent of both the !hold. conductor rand the pair of'line or talking conductors in order "to minimize the return of -swit'ching noises overithe line conductors tothe associated switchboard.

iiAnoth-er object-of the invention isto provide ina-repeaterswitchingiarrangement of the chareeter-noted, ani-mproved relay network selectively controlled to receive switch setting digits :f-romthe switchboard and to return supervisory signals and controls back toithe switchboard.

A1iurth'erobject of the invention is to provide vina repeater switching arrangement of the character-noted, ra'ntimproved relay network that ineludes-ta source of current supply independent of *theexchange batteries in two interconnected exv'c anges so that satisfactory "operation of the wr'e pe'atersiinlthe' two exchanges is obtained not- -withstanding :an under voltage condition of the exchange: batter in one of the exchanges.

-Further "features of the invention pertain to the "particular arrangement of the circuit ele- .ments of the:s'ystem, whereby the--above-out1ined --and additional operating'features thereof are at ings, in which Figure 1 is a schematic diagram or,

ax-telephone system embodying the present inven- :-tion and illustrating the general-arrangement of the apparatus incorporatedtherein; Figs. 2 tot, inclusive; takento'gether, illustrate the details of -.certa'in :of the apparatusincorporaJted in-the .;telephone, system, which apparatus has embodied thereinthe ieaturesoiatheinvention as, briefly "outlined above; and Fiat is a block diagram illustrating the mode of combining. Figs..2 to '.'6,

' inclusive, to form a unified circuit diagram.

More particularly, Fig; :2 .illustratesvthe details oi one of the cord circuits'disposed at the switch- -board in-one of the oiiices, :aswell: as the details .of

' one of the selectors accessible. thereto; Fig.3 i1lus-.

"ltr'ates 'the d'etaiIs et/one =of the repeatersdisposed in the one office mentioned; Fig. 4 illustrates the details of oneof the repeaters disposed in another of the offices; Fig. 5 illustrates the details of one or the incoming selectors disposed in the other #oifice; and Fig. 6 illustratesthe details of oneof "the toll selector repeaters disposed in the other 'ofiice.

Referring .now more particularly to Fig. 1 -of the drawings there is illustrated an automatic telephone system comprising two offices Hi and 2-55. The office it isof the automatic type serving a number of subscriber substations, including-the usubscriber substation T2535, and comprising a cswitchbhardiiifl of the manual dial type. Like wise,;theoffice 20 is of 'the automatic type serving .gaimunberiof subscriber substations, including the {subscriber substation TQM,- and comprising a switchboard :iit fl of the manual dial type. The -ofiices iii andZtl interconnected by a group pftrunksincluding the trunkt it, as well as by a potentiometer conductor Ctilil that is utilized for al lpurpose more fully explained hereafter. The apposite end :of the trunks 3%, etc., terminatein .rep'eaters respectively disposed in the oflice l8 L tandiiil, thetru nktfio terminating in the repeaters 'dtaandytllc respectively disposed in the offices l0 and 2t. #Gne; end of the potentiometer conductor C lfill is connected via a, pluralityof resistors 49L -etc., sto ground potential in the office 23; while the other end or the potentiometer conductor "Ct-9i} is "connected via a pluralityof resistors 39L .letc, to the negative terminal of a voltage regulated generatorsfiz disposed in the office It; the positive'term-inal of the generator 362 being conenected to groundpotential in the office it. Finally ground potentials in the oiiices it and '23 are econnected togetherilia earth or a suitable conductor not shown, so-that there is substantially no voltage difference therebetween.

iThe oiiice it also comprises a group of selectors, including the selector tfilhaccessible to the switchboardfislliand havingaccess to the group oi reeaters, including-(the repeater ttll. Each-of the repeaters 3Et, etc.,.;is provided with an incoming selector .205, etc. individual thereto and having accesstoa group .of toll selector repeaters, including the toll gselector repeater .202. Also the ofiice :rill-v'eorn-prises plurality of groupsof toll connectors, one of the groups including the toll conanectoni ls havingaccess to the groupbf'subscriber substations, including the subscriber substation 2M. -Further the office til comprises a tgroup of ring-dowa trunk circuits, including the rins-flown trunk circuit 2%, accessible. to the switchboard 210. Further the toll selectorrepeaters 204, etc., have access to the groups of toll connectors and to the group of ring-down trunk circuits. Finally, each subscriber substation T201, etc., has a subscriber line 202, etc., extending thereto that is provided with a line switch, not shown, individually associated therewith for the purpose of providing access to an outgoing switch train, not shown.

Similarly, the ofiice 20 also comprises a group of selectors, including the selector 521, accessible to the switchboard 510 and having access to the group of repeaters, including the repeater 400. Each of the repeaters 400, etc., is provided with an incoming selector 500, etc., individual thereto and having access to a group of toll selector repeaters, including the toll selector repeater 000. Also the office 20 comprises a plurality of groups of toll connectors, one of the groups including the toll connector 603 having access to the roup of subscriber substations, including the subscriber substation T69 1. Further the office 20 comprises a group of ring-down trunk circuits, including the ring-down trunk circuit 503, accessible to the switchboard 510. Further the toll selector repeaters 600, etc., have access to the groups of toll connectors and to the group of ring-down trunk circuits. Finally, each subscriber substation T50 I, etc., has a subscriber line 602, etc., extending thereto that is provided with a line switch, not shown, individually associated therewith for the purpose of providing access to an outgoing switch train, not shown.

Preferably, the switchboards M and I0 are identical; the switchboard 210 comprising, as shown in Fig. 2, a plurality of cord circuits 2l0', etc. The cord circuit 216' comprises a rear plug Pi? l i and a front plug P2 I 2', a manual dial D210, a talk key K233, a dial front key K215 and a ring front key K205. Also the cord circuit 2I0' comprises a. rear supervisory lamp, not shown, associated with the rear plug P2 l I and a front supervisory lamp L265 associated with a front plug P2 5 2', and a relay group including two ring relays R222 and R230, a pulse relay R240, a front supervisory relay R256 and a dial relay R250. Finally, the switchboard 2l0 comprises a headset 283 that may be connected by the talk key K264 to the cord circuit 210'.

Preferably, the selectors 200, 25 I etc., are identical; the selector 203 comprising, as shown in Fig. 2, an incoming trunk 220 terminating in a jack 522% disposed at the switchboard 2l0 and provided with an associated busy lamp L220. Also the selector 20E} comprises a relay group includin a test relay R230, a pulse relay R240, a hold relay R2523, a transfer relay R200 and a busy relay R235. Further the selector 200 comprises a Strowger mechanism including four wipers 2, 212, and 21 3, a vertical magnet M215 for driving the wiper carriage step by step in the vertical direction away from its normal vertical position, a rotary magnet M213 for driving the wiper carriage step by step in the rotary direction I away from its normal rotary position, and a release magnet M213 ior'releasing the wiper carriage and for causing it to be returned to its normal rotary and vertical positions. Also associated with the Strowger mechanism are three sets of switch springs S213, S200 and S28l that are operated when the wiper carriage is driven one step in the vertical direction away from its normal vertical position, and three sets of switch springs Preferably the repeaters 300, 4&0, etc., are identical; the repeater 300 comprising, as shown in Fig. 3, an incoming trunk 3m and a repeating coil 38;} operatively connected to the trunk 390. Also the repeater 303 comprises a relay group including a busy relay R339, a seize relay R340, a control relay BN5, a supervisory relay R350, two ring control relays R355 and R360, two control relays R335 and R315 and a signal relay R315. Likewise, the repeater 480 comprises, as shown in Fig. 4, an incoming trunk 410 and a repeating coil are operatively connected to the trunk "90. Also the repeater 403 comprises a relay group including a busy relay R 130, a seize relay R l iil, a control relay R445, a supervisory relay R053, two ring control relays R455 and R460, two control relays R435 and R415) and a signal relay R415. In the repeaters Silt and 400, the lower windings of the signal relays R315 and R415 are respectively bridged across the resistors 39! and 491 included in the potentiometer connection comprising the potentiometer conductor C490. It will be understood that in a similar manner the lower windings of the signal relays in the other pairs of repeaters, not shown, are bridged across the pairs of resistors 392, 492 and 393, 403, etc. Finally, it is noted that the voltage regulator 362 disposed in the oflice it may be of any suitable type producing a closely regulated potential of approximately 48 volts. Also in this regard it will be understood that in the offices [0 and 20, the battery voltage is approximately 48 volts, the positive terminal of battery voltage being indicated as connected to ground potential.

Preferably, the incoming selectors 205, 500, etc., are identical; the incoming selector 5G0 comprising, as shown in Fig. 5, an incoming trunk 420 and a relay group including a test relay R530, a pulse relay Refill, a hold relay R550, a transfer relay R560 and a busy relay R505. Also the incoming selector 509 comprises a Strowger mechanism including four wipers 51l, 512, 513 and 514, a vertical magnet M515 for driving the wiper carriage step by step in the vertical direction away from its normal vertical position, a rotary magnet M516 for driving the wiper carriage step by step in the rotary direction away from its normal rotary position, and a release magnet M518 for releasing the wiper carriage and for causing it to be returned to its normal rotary and vertical positions. Also associated with the Strowger mechanism are three sets of switch springs S519, S530 and S581 that are operated when the wiper carriage is driven one step in the vertical direction away from its normal vertical position, and three sets of switch springs S582, S533 and S53 1 that are operated when the wiper carriage is driven eleven steps in the rotary direction away from its normal rotary position.

Preferably, the toll selector repeaters 20 i, 500, etc., are identical; the toll selector repeater 800 comprising, as shown in Fig. 6, an incoming trunk 610 and a repeating coil 525. Also the toll selector repeater 600 comprises a relay group including a test relay R328, a pulse relay R330, a hold relay R635, a transfer relay Rli lll, a local relay R645, a toll relay R550, a toll answer relay R030, a local answer relay R505, and a ring relay R5310. Also the toll selector repeater 602 comprises a Strow-- ger mechanism including three wipers 551i, E82 and 583, a vertical magnet M634 for driving the 'wiper'carriage step by step in the vertical direction away from its normal vertical position, a rotary magnet M585 for driving the wiper carriage step by step in the rotary direction away battery potential.

from its normal rotary position, and a release magnet M681 for releasingithe .wiper carriageand for causing it to be returned to its normal rotary andvertical positions. Associated with'the Strow- 'ger mechanism are'three sets of switch springs S688, S0891and S690 that are operated when the wiper carriage is driven one step in the vertical direction away from its normal vertical position,

two sets of switch springs SSO! andSBQZ-thatare operated when the wiper carriage is driven eleven steps in the rotary directionaway from its normal rotary position, and aset of switch springs $693 that is operated when the'wlper carriage is driven in the vertical direction to a level in the associated contact bank wherein a group of trunks extending to a group of toll connectors is terminated.

.Finally, in the offices Iii and zt the toll connectors203, tilt, etc, are of the conventional Strowgertype; the ring-down trunk circuits 2.00,

508, etc, are of any suitable type; the line switches, not shown, associated with the subscriber lines 202, 302, etc., may be of any suitable type; and

the subscriber substations "1120!, T60l, etc., are

provided with conventional subscriber substation apparatus.

A better understanding of the connection and arrangement of the apparatus incorporated in the telephone system will befacilitated from a consideration of the extension of the various calls involving the cfiices l .and .20.

First considering the extension of a call from the calling switchboard 2H3 .in the office Hi to a called subscriber substation, such for example, as the subscriber substation T60I in the ofiice 20,

the operator at the callingswitchboard em first selects an idle cord circuit, such for example,.as the cord circuit 2| 0 and inserts'the front-plug LP2I2 thereof into the jack terminating a trunk extending to an idle one of the selectors in the group, including the selector 200. At this time assuming that the selector is idle, battery potential via the upper winding of'the transfer relay iRZiill and the set of switchsprings S219 is applied to the control conductor C223! of the incoming trunk .2229, thereby to short-circuit the.

busy lamp L220 indicating to the :operator at the calling switchboard 280 the circumstance noted.

-l\low assuming that the front plug ,-P2l2' is inserted into the jack J 220 terminating the incomingutrunk. 220, the contacts of the jack J220 are;

closed completing a circuit for illuminating the busy lamp L226 in order to indicate the busy condition of the selector 200 at this time.

"Alsowhenthe front plug P2 i 2" is inserted into the jack J 220 a series circuit is completed for ener- ,gizingthe winding of the front supervisory relay R250 in the cord circuit M0 and thewindingtof the pulse relay R2 10 in the selector 200; this'circuit extending from ground potential by way of the" winding of the pulse relay R240, the 0011-, tacts 234, the EC conductor C224 of the incoming trunk 220, the sleeve of the jack J 22.0, thesleeve of the fro-nt'plug 2H2, the contacts 283 and the winding of the front supervisory relay R250" to thus completed, the front supervisory relay 7325B and the pulse relay R2 50 operate. Also the ap- R2ii0in order to cause the latterrelay to operate. .Upon-loperating the front supervisory relay When this series circuit is;

56 illuminating the lfront [supervisory :lamp E2667, ithereby to indicate the circumstance that the -.call extended .via the .frontplugBZJ 2' has :not yet :been answered. Uponoperating the pulse relay R240 completes, at'thecontacts 2 a circuit, including the contacts 235, for operating the ;hold relay R253. Upon operating :the hold relay=R250 completes, .at ithe contacts 251, a multiple path ,forrapp lying ground potential to the controlcon- --ductor: C223 of the incoming trunk 22c; and completes, .at the contacts 25:3, a circuit for energizing the lower winding of the test relay R230 in: order to .render'thelatterrelay exceedingly fast to" operate when the upper winding thereof is subse- ;quently energized, the :test relay R230 being of :the po larized type.

The operator at the calling switchboard 210 =0perates the dial front key K215 andthen-pro- :,ceeds to dial the first digit of the directoryznum- :ber of the called subscriber substation Tl by appropriately manipulating the finger wheel of the dial D2-l0'. 'When'the finger wheel of the dial D238 is operated away from its normal position, the ;off-,normal contacts 1 212 are operated completing a .circuitincluding the first contacts of the dial front key K215 for operating the dial relay R260. Upon operating the dial1relay R260 completes, at the contacts 261?, zaicir cult, including the impulse contacts 21! of the dial -D2|0,.for operating the pulse relay R240. Also the dial relay R260 completes, {at the contacts 262' a path, includingthesecond contacts of the :dial front key EK215, the contacts 241 and the resistor 26'! for applying battery poten- 11316.1 to the sleeve of the front plug P2l2"; and interrupts, at. the contacts 263, the previously traced circuit for energizing in seriesthe winding of the front supervisory relay R250 and the -winding of the pulse relay R240. Accordingly, the front supervisory relay R250 restores and the pulse relay R240 is retained in its operated position via the alternative circuit for energizing the winding thereof, including the EC conductor 0224 0f the incoming trunk 220, the contacts 2M of the operated pulse relay R240 and the resistor 261'. Subsequently, when the finger wheel of the dial D270 is released, the impulse contacts 21! thereof are openedand then closed repeatedly a number of times in accordance with the impulses of the first digit of the directory number of the called subscriber substation 'IBlll.

Accordingly, the dial D210 transmits, at the impulse contacts 2H'-thereof, the impulses of the present digit causing the pulse relay R240 to follow. During the transmission of the impulses of the present digit, the off-normal contacts 272' of the dial D210 are retained in their closed position retaining operated the dial relay R280. Upon restoring the front supervisory relay R250 interrupts, at the contacts '25l' the circuit for illuminating the front supervisory lamp L266; however, without effect at this time.

Accordingly, the pulse relay R240 following the impulses of the present digit alternately transmits battery and ground potentials, at the contacts 24f and 242, over the sleeve of the front plug P2l2 and consequently theEC conductorC224 of the incoming trunk 220; whereby the pulse relay R240 follows. More particularly, each time the pulse relay Rz w' restores, itinterrupts, at thecontacts' 2M, the path for .connecting battery potential to the sleeve of the front plug P2 |2',; andcompletes, at the contacts 242' ,a, substantially identical pathjfor connecting "Elm-"completes, at the contacts 251 flea circuit for ground; potential to the. sleeve of xthe:frontpzplug ,P2l2; whereby the winding'of the pulse relay R240 is deenergized and then short-circuited causing the latter relay to restore after a very brief time interval. Conversely, each time the pulse relay R240 operates, it interrupts, at the contacts 242, the path for connecting ground potential; and recompletes, at the contacts 241, the path for connecting battery potential to the sleeve of the front plug P2l2; whereby the pulse relay R200 reoperates. Each time the pulse relay R240 restores and then reoperates, it interrupts and then recompletes, at the contacts 24l,

the circuit for retaining operated the hold relay R250; whereby the latter relay is retained in its operated position during impulsing as it is of the slow-to-release type. Also each time the pulse relay R240 restores and then reoperates, it completes and then interrupts, at the contacts 242, a circuit, including the contacts 235, 254 and 263, for energizing the lower winding of the transfer relay R260 and for operating the vertical magnet M210; whereby the transfer relay R200 is retained in its operated position during impulsing as it is of the slow-to-release type; and the vertical magnet M215 is operated repeatedly in order to drive the wiper carriage of the Strowger mechanism step by step in the vertical direction.

At the conclusion of the first digit, when the finger wheel of the dial D210 is returned to its normal position, the impulse contacts 21H are retained in closed position retaining operated the pulse relay R200; and the off-normal contacts 212 are opened in order to cause the dial relay R260 to restore shortly thereafter, the latter relay being of the slow-to-release type. Upon restoring the dial relay R260 recompletes, at the con-- tacts 263, the previousl traced series circuit for energizing the winding of the front supervisory relay R250 and the winding of the pulse relay R240, thereby to eiiect reoperation of the front supervisory relay R250 and to retain the pulserelay R200 in its operated position. Upon reoperating the front supervisory relay R250 again. completes, at the contacts 25l', the circuit for illuminating the front supervisory lamp L200" in order again to indicate that the present call. extended via the front plug P2i2' has not been answered. When the wiper carriage of the Strowger mechanism is driven one step in thevertical direction away from its normal vertical position, the sets of switch springs S219, S230 and S28! are operated. More particularly. theset of switch springs S218 is operated in orderto interrupt the circuit for energizing the upper winding of the transfer relay R260. Accordingly, shortly following the conclusion of the first digit, the pulse relay R200 being retained in its operated position, the transfer relay R250 restores, as it is of the slow-to-release type. Upon. restoring the transfer relay R260 interrupts, atthe contacts 203, a further point in the multiple circuit for energizing the lower winding thereof and for operating the vertical magnet M215; and. completes, at the contacts 23 a circuit, including the contacts Ell, the set of switch springs S280 and the contacts 202 and 235, for operating the rotary magnet M210. Upon operating the rotary magnet M216 drives the wiper carriage of the Strowger mechanism one step in the rotary direction; and interrupts, at the contacts- 211, the operating circuit therefor. Accordingly, the rotary magnet M216 restores in order torecomplete, at the contacts 211, the operating circuit therefor. Thus the rotary magnet M211 operates buzzer fashion in order to drive the wiper carriag of the Stowger mechanism step by step in the rotary direction; whereby the test relay R230 tests the idle or busy condition of the individual incoming trunks in the previously selected group, including the incoming trunk 310 extending to the repeater 300; the group of incoming trunks, including the incoming trunk 3l0, being selected by the Strowger mechanism in response to the first digit. More particularly, when the wiper set of the Strowger mechanism selects the first trunk in the group mentioned, the idle or busy condition thereof is tested by the test relay R230 via a path extending from ground, at the contacts 25!, and including the upper winding of the test relay R230 and the contacts 252 and 262 and the control wiper 213 of the wiper set. Specifically, in the event that the first trunk mentioned is busy, ground potential appears upon the control conductor thereof completing a substantially identical path for short-circuiting the upper winding of the test rela R230; whereby the latter relay remaining in its restored position, permits continued operation of the rotary magnet M216 in the manner previously described.

. Now assuming that the incoming trunk 3l0 is the first idle trunk in the group mentioned, battery potential appears upon the control conductor C3|3 thereof via a path including the contacts 33! and 34! and the upper winding of the seize relay R340 in the repeater 300. Accordingly, when the wiper set of the Strowger mechanism selects the incoming trunk 3l0, a circuit substantially identical to that previously traced is completed for energizing the upper winding of the test relay R230 in the selector 200 causing the latter relay to operate exceedingly fast as it is of the polarized type. Upon operating the test relay R230 interrupts, at the contacts 235, the circuit for operating the rotary magnet M216 in order positively to prevent further operation in the rotary direction of the wiper set of the Strowger mechanism. Also the test relay R230 completes, at the contacts 232, a holding circuit, including the grounded control conductor C223 of the incoming trunk 220, for energizing the intermediate Winding thereof; and interrupts, at the contacts 235, a multiple circuit for energizing the winding of the hold relay R250 in order to cause the latter relay to restore shortly thereafter, it being of the slow-to-release type. Also the test rela R230 interrupts, at th contacts 234, the circuit for retaining operated the pulse relay R240; and completes, at the contacts 233, a connection between the EC conductor C224 of the incoming trunk 220 and the EC wiper 214 of the Strowger mechanism. Also the test relay R230 completes, at the contacts 23!, a path, including the contacts 262, for applying ground potential to the control wiper 213 of the Strowger mechanism; and completes, at the contacts 236 and 231, connections between the line conductors C221 and C222 of the incoming trunk 220 and the line wipers 211 and 212 of the Strowger mechanism.

At this time, direct ground potential is applied via the control wiper 213 of the Strowger mechanism to the control conductor C3l3 of the incoming trunk 3E0 completing a circuit, including the contacts 331 and 30 l for energizing the upper winding of the seize relay R3 30 in the repeater 300 in order to cause the latter relay to operate. Upon operating the seize relay R340 interrupts,

75 at the contacts 3, a path, including the contiacts 33l-and 332; for short-circuiting the lowerwinding thereof whereby the upper and lower windings of the seize relay R340 are energized in seriesv via the contacts 332 from the control conductor 6M3 of the incoming trunk 3M in order to retain the seize relay R3 in its operated position. Also the. seize. relay R545 completes, at the contacts 3&3, a connection between thev EC conductor (33M of the incoming trunk 31B and the lower winding of the supervisory relay R359. More particularly, at this time, the upper winding of the supervisory relay R350 is shortcircuitedvia a path including the contacts 311; and the lower winding of the supervisory relay R3356 is energized in series, with the winding of the. front supervisory relay R255 over the previously tracedcircuit, including the EC conductor 63M- of the incoming trunk 3H] and the EC conductor C226 oi. the incoming trunk 2253. When this series circuit is completed the front supervisory relay R256 retained in its operated position and the supervisory relay R358 is operated. Specifically, the supervisory relay R358 is operated since the lower winding thereof is energized and the upper winding thereof is short-circuited, the supervisory relay R35!) being of the. differential type, Upon operating the supervisory relay R350 interrupts, at the contacts 35!, a normally completed path, including the contacts 312 and the impedance.- element 518-, for short-circuiting the upper winding of the signal relay R375; and interrupts, at the contacts 35!, a multiple path, including the contacts 372 and the intermediate winding of the signal relay R3l5, for applying ground potential tothe simplex conductor C385. Also upon operating the supervisory relay R350 completes, at the; contacts 352, a circuit, including the resistor 353, the contacts 312. and the impedance element 318, for energizing the upper winding of the signal relay R315; and a multiple path, including the contacts M2, for applying battery potential by way of the resistor 353. and the intermediate winding of the signal relay R315 tothe simplex conductor C385. The simplex conductor C335 is connected via the windings, 3&3 and 38d of the repeating coil 3% and the line conductors of the trunk 395 and the windings 485and iihi of the repeating coil itllto the simplex conductor (M85; which simplex conductor C485 is-connected: via the intermediate: winding of the signal relay R il5 in the repeater tilt and thecontactsJi'iZ and. t5lto ground potential. Ac- Chirdingly, the intermediate windings of. the signal relays and are energized in series circuitrelation, also. the upper winding of the signalrelay BN5 is short-circuited via a path, including the, contacts Q51 and 4,72 and the impedance element ill-,8. Further the lower winding of, the signal. relay R3l5 is energized by the voltage. drop. developed across the, resistor 3.9! included. in the potentiometer circuit; and the lower winding of the signal relay R475 is energized by the voltage drop developed across the resistor till included in the potentiometer circuit.

Accordingly, at this time the upper and lower windings or the signal relay R315 are energized in cumulative relation and in oppositionto the intermediate winding, thereof whereby thesignal relay does not operate. On the other hand, the. upper winding of. the signal. relay R415 is short-circuited while the intermediate and lower windings thereof are energized in opposing relation; however. since the. intermediate winding of the signal. relay Rt'lii predominates over the lower. winding thereoi. the signal relay R475 operates. Upon operating the signal relay R415, interrupts, at the contacts 411, a normally com pletedpath for short-circuiting the upper winding of the supervisory relay R450 and. a multiple path including the lower winding of the supervisory relay R 350- and. the-contacts M4 for applying ground potential to the EC conductor C424 of the incoming trunk 62:0 extending tothe incoming selector 509.. Further the signal relay- R415 completes, at the; contacts till, a circuit for energizing the upper winding of the supervisory relay R iiiil in series with the winding ofthe control relay RM5, and amultiple path for applying. battery. potential by wayof thewinding ot the control relay R445, the lower winding of thev supervisory relay B l-55 and the contacts 4415. to the EC. conductor C424. of the incoming, trunk 420. At this time ground. potential in the; in-.. coming selector 5504s connected via the winding of thezpulsev relay R5 lll therein and the contacts 534. to the. EC. conductor C42 8 ofthe incoming trunk- 428. Accordingly, the lower winding of the supervisory relay, R458, in the repeater Mil is energized in series with the winding of the, pulse relay lzt5 lilv in the incoming selector 50d; whereby the pulse relay RMlloperates. However, the supervisory relay R 359. does not. operate since both. the. upper and, lower windings, thereof, are energized and this relay isof thedifferential type.

Upon operating the. control relay EH45 completes, at-the. contacts- 445,. a, circuit, including the contacts. M2, for operating; the busy relay R430; Upon operating the busy relay R450. interrupts, at the contacts 43L a. path, including. the contacts Ml, for applying battery potential, via the upper winding or the seize, relay R640. tothe control conductor 0M3 of the incoming trunk 4M; interrupts, at, the'contacts 4H and 432, a normally completedv path for short-circuiting the lower winding of the seize relay R449; and completes, at. the. contacts, 443,, a path for applying ground potential to the control conductor CAI-3 of the incoming trunk. 4H),. This application of ground potential, to, the control conductor CH3 marks the. incoming trunk M5 and. consequently the repeater Mill, as busy.- to the selectors 52 l, etc., having access thereto. Also, the busy relay R430 completes, at the contacts 434, a. path for applying ground potential tothe control conductor C423; of the outgoing trunk 4221, thereby to com,- plete acircuitincluding, the set of switch springs $519, for energizing. the upper winding of the transfer relay R550 in the incoming selector 5D!) in. order to cause the latter relay to operate. Upon operating the pulse relay R540 completes, at the contacts, 54!, av circuit, including thecontacts, 53.5, for operating the hold relay R555. Upon operating the, hold relay R550 completes, at the contacts 551,. a multiplepath for applying ground potential to the control conductor C625 of the outgoing trunk 425; and completes, at the contacts 553, a circuit for energizing the lower winding of the test relay R530 in order to render the latter relay exceedingly fast tov operate, when the. upper winding, thereof, is subsequently energized, it, being of the. polarized, type. At this time the selector 200. has responded to the, first digit, ot thedirectory number of the called sub.- scriber substation, T50 I dialed at. the calling Switchboard 2 It to select the incoming trunk 3M extending to. the, repeater 300; the repeater 385 has seized the repeater 455 over the trunk 3-90; and the. repeater 483 hasseizedthe incoming selector 5110, over the outgoingv trunk 420, A0-

cordingly, the incoming selector 5053 1'sv in readi-s ness to receive the second digit of the directory number of the called subscriber substation T601.

The operator at the calling switchboard 210 then proceeds to dial the second digit of the directory number of the called subscriber substation T601; whereby the dial D210 in the cord circuit 210' transmits alternate battery and ground impulses over the sleeve of the front plug P2 42 in the manner previously explained. More particularly, each time battery potential is removed from and ground potential is applied to the sleeve of the front plug P212 and consequently to the EC conductor C224 of the incoming trunk 220, the previously traced circuit for energizing the lower winding of the supervisory relay R350 is interrupted and a substantially identical path for short-circuiting the lower ,winding of the supervisory relay R350 is completed, causing the latter relay to restore after a very brief time interval. Conversely, each time ground potential is removed from and battery potential is applied to the sleeve of the front plug P212 and consequently the EC conductor C224 of the incoming trunk 220, the path for shortcircuiting the lower winding of the supervisory relay R350 is interrupted and the circuit for energizing the lower winding of the supervisory relay R350 is completed; whereby the latter relay operates. Accordingly, the supervisory relay R350 follows the impulses of the second digit dialed at the calling switchboard 210. Each time the supervisory relay R350 restores, it interrupts, at the contacts 352, the circuit for energizing the upper winding of the signal relay R315 and the multiple circuit for energizing the intermediate winding of the signal relay R315 in series with the intermediate winding of the signal relay R415; and completes, at the contacts 351 the path for short-circuiting the upper winding of the signal relay R315 and the multiple path for shortcircuiting the'intermediate winding of the signal relay R315 in series with the intermediate winding of the signal relay R415. Accordingly, the signal relay R315 is retained in its restored position and the signal relay R415 follows the impulses of the present digit. Each time the signal relay R415 restores, it interrupts, at the contacts 410, the circuit for energizing the winding of the control relay R445 in series with the upper winding of the supervisory relay R450 and the multiple circuit for energizing the winding of the control relay R445 in series with the lower winding of the supervisory relay R450 and the winding of the pulse relay R540; and completes, at the contacts 411, the path for short-circuiting the upper winding of the supervisory relay R450 and the multiple path for short-circuiting the lower winding of the supervisory relay R450 in series with the winding of the pulse relay R540; whereby the supervisory relay R450 is retained in its restored position and the control relay R445 restores and the pulse relay R540 restores after a very brief time interval. Conversely, each time the signal relay R415 operates, it interrupts, at the contacts 411, the path for short-circuiting the upper winding of the supervisory relay R450 and the multiple path for short-circuiting the lower windinglof the supervisory relay R450 in series with the winding of the pulse relay R540; and recompletes, at the contacts 410, the circuit for energizing the winding of the control relay R445 in series with the upper winding of the supervisory relay R450 and the multiple circuit for energizing the winding of the control relay R445 in series with the lower winding of the supervisory relay R450 and the winding pulse relay R540 in order to retain the supervisory relay R450 in its restored position and to effect operation of the control relay R445 and the pulse relay R540. Thus the signal relay R415 repeats to the control relay R445 and the pulse relay R540; whereby the relays mentioned follow the impulses of the present digit. Each time the control relay R445 restores and then reoperates it interrupts and then recompletes, at the contacts 446, the circuit for retaining operated the busy relay R430; whereby the latter relay is retained in its operated position during impulsing as it is of the slow-to-release type. Each time the pulse relay R540 restores and then reoperates, it interrupts and then recompletes, at the contacts 541, the circuit for retaining operated the hold relay R550; whereby the latter relay is retained in its operated position during impulsing as it is of the slow-to-release type. Also each time the pulse relay R540 restores and then reoperates, it completes and then interrupts, at the contacts 542, a circuit, including the contacts 535, 554 and 553, for energizing the lower winding of the transfer relay R550 and a multiple circuit for operating the vertical magnet M515.

The remainder of the operation of the incoming selector 500 in response to the second digit of the directory number of the called subscriber ubstation T00l is essentially the same as that of the selector 200 previously described. Specifically, the wiper set of the Strowger mechanism in the incoming selector 500 is operated to the level of the group of trunks in the associated contact bank including the incoming trunk 6H3 extending to the toll selector repeater 000. At the conclusion of the present digit the pulse relay R540 is retained in its operated position and shortly thereafter, the transfer relay R500 restores effecting operation of the rotary magnet M515. As the wiper set of the Strowger mechanism is rotated the individual incoming trunks in the group, including the incoming trunk Hi0, are tested by the test relay R530; and when an idle trunk in this group is selected by the wiper set the test relay R530 is operated to efiect the restoration of the pulse relay R540 and the restoration of the hold relay R550 shortly thereafter, the latter relay being of the slow-to-release type. Assuming that the incoming trunk 510 is the first idle trunk in the group mentioned when it is selected by the wiper set of the Strowger mechanism, the test relay R530 is operated as previously noted. Upon operating the test relay R530 interrupts, at the contacts 535, the operating circuit for the rotary magnet M516 and the circuit for retaining operated the hold relay R550; interrupts, at the contacts 534, the circuit for retaining operated the pulse relay R540; and completes, at the contacts 532, a holding circuit including the grounded control conductor C423 of the out-going trunk 420, for energizing the intermediate winding thereof. Also the rest relay R530 completes, at the contacts 531, a path for applying ground potential via the contacts 562 to the control wiper 513; completes, at the contacts 533, a connection between the EC conductor C424 of the outgoing trunk 420 and the EC wiper 514; and completes, at the contacts 536 and 531, connections between the line conductors C42! and C422 of the outgoing trunk 420 and the line Wipers 515 and 512.

The application of ground potential to the con trol wiper C513 completes a circuit, including the control conductor C013 of the incoming trunk of the accuses:

610 and the set; of: switch. springs. $688, for ensergizing the upper winding of the transfer relay R649? iIIaO-Idl to cause the; latter relaytol operate; At this time. ground: potential is. connected via theicontacts 643 and fir'i i to the junctionbetween the upper and lower windings of the pulse. relay R6311, the other terminaL of. the: upper: winding of thepulse relay R638 being connected to ground potential and the other terminal of the lower winding of the pulserelay R630 being connected. to the EC conductor C6 of the. incoming trunk Bil-E Accordingly, a path iscompleted for'shortzcircuiting" the upper winding of the pulse relay R638; and a: circuit is. completed for energizing the: lower winding of; the pulse relay R630 in. series with the lower winding of" the: supervisory;

relay R459 and" the winding of the control relay" R44 5. Accordingly, thepulse' relayRt-"sfl in the. toll selector repeater 5% is operated; thesuper visory rel'ay R456 in the repeater 4M is: retained in its restored position; and the control. relay H445 in the repeater tilt is retained in its operated position. Upon operating the. pulse relay R63il completes; at the contacts 63!, a circuit for operating the hold relay R635. Upon operating the hold relay R685 completes, at the contacts 636, a'multlple pathfor' applying ground potemtiat to the controlconductor C513 of the incom ing trunk 610: and completes, atthe contacts 638*, acircuitfor energizing the lower winding of the testarelay R162 0: inorder to renderthelatter relay exceedingly f ast te operate when theupperwinding thereof: is subsequently energized, the test relay R625 being of the polarized type; At this time thezi-ncoming selector 590 has responded to the second digitofthe directory numberof the called: subscriber substation Tfi'di to select the tol selector repeater 665 via the incoming" trunk Gill; and thetoll selector repeater Stilis conditioned to respond to" the third digit of the direc. tory number of the: called subscriber substation T601.

The. operator at the calling? switchboard 21B" then proceeds to dial: the third? digit of the direc torynumber-of the called substcribersubstation T601; whereby the supervisory relay R350 fol lows. repeating tothe signal relay R415; and the: signal relay R41 5. follows repeating to: the control relay R445 and to the pulse relay R538. During impulsing. the signal relay R315 and the super--. visory relay RAEI] are retained in their restored positions; Specifically,v the signal relay R 575 applies-alternately battery and ground potential via. the: previously traced path to the EC conductor 0424 or the outgoing trunk 32%]. and consequently totheEC conductor'cfii s of the. incomingtrunls. 6158 Each. time batter potential is removed from and ground'potenti'al is applied to the ECL conductor CBM, the circuit for energizing; the:v

lowertvinding of the pulsexrelayRfitt is interrupted? and a substantially identical: path for shorti-circuiting the-lower winding'thereof is compi et'ed whereby the pulse relay Rfitti restoresiaiter a: very brief time interval. Conversely; each time ground potential is removed from and battery potential applied to the EC- conductor 06M, thev path. for short circuiting the: lower winding of.

the pulse relay. R630 is interrupted and the cir. cuit 'for energizing the lower: winding thereof is completed; wherebythepulse relay R633 oper ates. Accordingly; the pulse relay Rtte' follows the: impulses ot the present: digit.

Each time the pulse relay RtSfi; restores and then reoperates, it: interrupts and. then recoinpistes. at the: contacts 83.11,. the circuit for: retain.-

ing operated: the hold. relay R535; whereby. the.

latter. relay is" retained in its operatedpositiorr during. impulsing; as. it is or theslow-to-release.

type. Also each time; the pulse relay R630 re:- stores. and thenreoperates; it completes andthen interrupts, at the contacts: 632,, a circuit,,includ1- ing. the contacts 639, for energizing the lower winding of: the transfer relay R640, and a multiple circuit; also including the contacts 624; tor operating thei'vertical magnet M654; Accord.- in'gl y, the transfer relay REM! is retained in its. operated. position during ilnp-ulsing as it is. of the slow-to-release. type and. the vertical magnet M684 is operated intermittently in order 170:. d'rive the wiper; carriage of the; Strowger mechar nisnrsteprby step inthev vertical direction. When: the wiper carriage. of the- Strowger mechanism:

is driven one step in the vertical direction away". from. its normal vertical position, the sets. of.

switch. springs S538, ease and S598 are operated. More particularly, the set of switch springs S588 is operated in order to interrupt the circuit for energizing the upper winding of the transfer relay R5 19; At this time the toll selector repeater 600 is controlled to cause the wiper set to select the group of trunks, including the trunk tilt extend-- ing to the toll connector 663-, the group of toll connectors, including the toll connector 603, having access'tothe group of subscriber linesincluding the subscriber line 692 extending to the called subscriber: substation Ttill. Also at this time the set of switch springs S693 is operated since the wiper. carriage is driven in the vertical direction away from its normal vertical position to select'the group of trunks, including the trunk 6&5, asthe present call is a local call. Specifically, theset of. switch springs. S593 is: operated to open the first contacts thereof included in a circuit.

for operating thetoll' relay R550 and to 'close the second contacts thereof included in a circuit for operating the local relay R645.

At the conclusion: of the third digit, the supervisory relay Bitter is retained in its operated position retaining operated the signal. relay R415; whereby the control relay R445 and the pulse relay R53?) are retained in their operated positions. The operated pulse relay REM causes the transfer relay R545): to restore shortly thereafter,

it being of the slow-to-release type. Upon re- 5 storing thetransfer relay Rfi lt completes. at the.

contacts 6M, a circuit, including the contacts 686, the. set of switch springs S588 and the contacts 621. and 631;, for operating the rotary magnet M685. Upon operating the rotary magnet M685;

drives the wiper carriage of the. Strowger mecha-- cessive trunks in the group, including the trunk B85, is tested: by thetest relay R828. First. assuming thatall of the trunks in. the group men-- tioned, and preceding the. trunk 535 are busy,

groundpotential appearsuponthe control conduc- I tors thereof; whereas battery potential appears:

upon the control conductor C628 of theidletrunk And-the Wiper set selects each of the busy trunks,v a. path, includin the control wiper 683-,

the: contacts M2 andfiS'l and the grounded, con,

tl'Ol'l conductor C853 of the. incoming trunk 61.9,.

Thus the. rotary magnet:

is completed for short-circuiting the upper winding of the test relayRiiZil, thereby positively to prevent operation of the latter relay. However,

when the wiper set selects the trunk 525 battery potential appearing upon the control conductor C688 thereof completes a substantially identical circuit for energizing the upper winding of the test relay R626; whereby the latter relay operates exceedingly fast as it is of the polarized type. Upon operating the test relay R626 interrupts, at the contacts 62 l the circuit for operating the rotary magnet M635; and completes, at the contacts 622, a holding circuit, including the grounded control conductor CBlS of the incoming trunk 6H], for energizing the intermediate winding thereof. Also the test relay R620 interrupts, at the contacts 624, a further point in the circuit for operating the vertical magnet M684; and completes, at the contacts 82E, a path, including the contacts 642, for applying ground potential to the control wiper 683 and consequently to the control conductor C568 of the trunk 665.

The application of ground potential to the control conductor C598 of the trunk 6135 efiects seizure of the toll conector 563. Also, at this time the operated hold relay R635 completes, at the contacts 636, a circuit for energizing the upper winding of the local answer relay R565 rendering the latter relay fast to operate when the lower winding thereof is subsequently poled in a predetermined direction, the local answer relay R665 being of the polarized type. Moreover, at this time the operated pulse relay R638 completes, at the contacts 633, a circuit, including the line wipers 58L $82, the contacts SH, 674, the windings 628, 629 of the repeating coil B and the contacts 651, for bridging the lower winding of the local answer relay R685 across the line conductors C686 and 068! of the trunk 6G5 extending to the toll connector Bill-l. Specifically, the line relay in the toll connector 693 is energized in series with the lower winding of the local answer relay R665 via the above-traced circuit; however, the direction of current in this circuit is not in the predetermined direction mentioned to pole the local answer relay R665 to operate. words, the local answer relay R685 is retained in its restored position although the line relay in the toll connector 6% is operative rendering the toll connector SE53 responsive to the next two digits dialed at the calling switchboard 2l0. Accordingly, at this time the toll selector repeater Bill] has operated in response to the third digit of the directory number of the called subscriber substation Ttili in order to select the trunk 605 extending to the toll connector 693, and the toll connector 683 is conditioned for operation.

The operator at the calling switchboard 2"] then proceeds to dial the fourth and fifth digits of the directory number of the called subscriber substation Tfilll, which digits are repeated between the repeaters Silll and Mill and then by the repeater Gilli to the toll selector repeater 600 in a manner identical to that described above in conjunction with the transmission of the third digit of the directory number of the called subscriber substation Tfilll to the toll selector repeater 600. Specifically, the pulse relay R638 first follows the impulses of the fourth digit mentioned retaining the hold relay R635 in its operated position during impulsing and effecting operation of the transfer relay R649 at the beginning of impulsing and retaining the transfer relay R648 in its operated position during impulsing. Upon reoperating the transfer relay R640 completes, at the" In other potential to the control wiper 583.

16 contacts 6M, an alternative'path, including the contacts 638, for applying ground potential to the control wiper 683; and interrupts, at the contacts M2, the original path for applying ground Also the transfer relay R640 completes, at the contacts t' il, a direct path, including the windings 628 and 529 of the repeating coil 625 and the contacts 651, for short-circuiting the lower winding of the local answer relay R565 in order positively to prevent operation of the latter relay during impulsing and to improve the impulsing circuit via the line wipers 68! and 682 between the toll selector repeater 600 and the toll connector 603. Moreover, each time the pulse relay R538 restores and then reoperates, it interrupts and then re completes, at the contacts 633, the loop circuit extending via the line conductors C685 and CS0! of the trunk 685 to the toll connector 603; whereby the line relay in the toll connector 603 follows the impulses of the present digit.

At the conclusion of the fourth digit of the directory number of the called subscriber substation Ttlll, the pulse relay REM is again retained in its operated position; whereby the transfer relay R648 restores shortly thereafter, it being of the slowtorelease type. Upon restoring, the transfer relay R349 recompletes, at the contacts M2, the original path for applying ground potential to the control wiper 683; and interrupts,-- at the contacts Ml, the alternative path for ap plying ground potential to the control wiper 683. Also the transfer relay R640 interrupts, at the contacts 54!, the path for short-circuiting the lower winding of the local answer relay R665; whereby the lower winding of the local answer relay R685 is again inserted in the loop circuit with the line relay ,in the toll connector 683. However, the local answer relay R665 is not operated at this time as the lower winding thereof is not properly poled. Accordingly, the toll se-- lector repeater 600 responded to the fourth digit of the directory number of the called subscriber substation TBUI received over the EC conductor 06M of the incoming trunk Gill and repeated this digit over the loop circuit including the line conductors 05GB and C68! of the trunk 695 to the line relay in the toll connector 693. In a similar manner the toll selector repeater 60% receives and repeats the fifth digit of the directory number of the called subscriber substation TSBl.

The toll connector 683 responds to the fourth;

and fifth digits mentioned in a conventional manner to select the subscriber lines 682 extending to the called subscriber substation Tfiill. The subsequent operation of the toll connector 683 is governed by the idle or busy condition of the called subscriber substation TEE)? at this time in a conventional manner.

First assuming that the called subscriber sub-;

station T50! is idle at this time, the toll connector 6&3 operates to project ringing current over the subscriber line 602 and to return ringback tone current over the line conductors C606- and C69? of the trunk 605. This-ring-back tone current received over the line conductors of the trunk 665 is repeated by the repeating coil 625 over the line conductors of the incoming trunk' 6H! and consequently over the line conductor of the outgoing trunk 42%; which ring-back tone current is repeated by the repeating coil 48!? over the trunk 5390 and then repeated by the repeating coil 380 over the line conductors of the incoming trunk 3m and consequently over the line.

conductorsiof the incoming trunk 22a to thecord 17.; circuit- 2 I 0, and accordingly to the? headset .2 63. attthe. calling switchboard 2-] ll. indicating. to. the. operator, thereat. that the. called. subscriber substation 'IGlli: is-being rung, at this time.

When the. subscriber; at. the called; subscriber substation. T60]; answersthe call the toll cone nector 603;- operates l to reverse the polarity over the loop; circuit; including the. line conductors G605: and (1681?; of. the; trunk; 685;; whereby the lower: windingof; the local answer relay Rlilie, is poled: to; operate. Upon operating: the; local; answer relay R6515. completes. at theicontacts2 the; at circuit including the. second; contacts of the. set; or; switch; springs; S593; for: operating; the local relay R645. Uponoperating the local re.- lay R6 completes, atthe contacts 53%,... 215.161.0101 ing circuit, including the; grounded; (30111312015 condllGtOI'ICB. I 3;. of. the: incoming trunk,- Blll; for ener gizing; the winding; thereof; AISQJllhBj local-- relay R64 51111136111113; at the contacts .54 8, the, path; for;- connecting: ground;= potential to the junction baa tweenithe upper and-lower;windingsioi the pulse. relay R530; andlcompletes,-,at the; oontactstsh, a circuit. including'the contacts 6.5.44 31151163 33 for. energizing the. lower: winding :of', the transfer; relay R6401: in. series with the: upper; winding oi. thepulse relay. R6391; and. a. multiplepath .for: plying: battery' potential by way of the; lower windingzofrthe transferrelay R848 andthe lower;- winding: of: the..p,ulsee relay Renato; the EC con ductonCfiM ofithe incoming trunlc Sill: At this timethe upper windingof therpulse-relay REM-is.- no;. longer shortscircuited; but rather. it is, energized': in series: with. the lowerwinding; of the. transfer relay R6405 whereby the. pulse, relay R530 is retained in-..its operated. position. How. ever; .theitransier rel-ay-Etfiwisnotoperated when, the lower: winding. thereofi is; thus energized. in. serieswith therupper winding of the; pulse relay 363D. since the transfer. relay 36%;. is. of; the marginaltype, Moreover, the-applicationof ba tery potential;via.theglower;winding of the trans?" fen-relay Rfiililtand the lower: winding ot the pulse relay 3630;. completes a seriesv path; for shortcircuiting the lower;- winding, of. the. pulse relay. Rhett; in series; with v the lower winding, of. thesupervisory' relay Reta. Specifically, the; wind. ingof the control .rel-ayRMfi is-energized, in.-scrie s withthe upper winding of, thesupervisoryrelay. R459. retaining; thecontrol; relay R445 inv itsoperatedposition; and. theupperwinding; of. the. pulserelay. Rfitili is" energized. in. series with the, lowen-winding'of, the transfer relay Reel). retain. ing; the pulse; relay; Rfitil; in its: operated. positioni but-preventing operation. of the transfer relay,- Rfidmas it is ofcthe marginaltype; However, the; intermediate voltage developedgat the, junction of. the upper. and. lower windings of the. pulse, relay R630. substantially matches; the intermediate: voltage: developedat the junction ofv the, upper andlowcr windings-oi the supervisory relaylRAfiu; whereby theI lower winding of the. pulse relay R630. and the lower winding or. the supervisory; relay R4 50 are. effectively shortcircuited. in. series as previously noted. Accordin y. since the-su ervisory relay-R450. is ofjthe. differential. typ e,.it operates: at: this time the upper. winding thereof being; energized and the lowerwindingthereoiibeing short-circuitedh Upon:operating thesuperyisory relay Rilillinterruptaat the contacts 451, he; path: for. shortrcircuitins; e Windin oi, tbs-signalrelay. R475. and the multiple circuit or. ener izing the. intermediate. winding, of. the. signal relay Run in SfiIiBSj-With theintermediate windingof. thezsignal. relay-R315... Also 13311851111? ing'current over the subscriber line 6832; and the.

ervisory. re1ay,R45ll completes, at. the. contacts a circuit, .including.the resistor 4.5.3; the. con tacts: i iil and.th.e impedance element; llil, for, energizing the; upper windingoi. the signal relay.

R illi anda multiple path for short-circuitingthe intermediate. winding of the signal relay R42 Erin.

serieswith the intermediate winding of the signal relay. Ptiilli; Accordingly, at thistime, theintermediate winding. ofthe signal relay is short-.

oircuited and the upper andlower windings, there of! are energizedin cumulative.- relation retaining;

the signal. relay R4335. in its; operated. position.

Similarly, the. intermediate. winding of the signal. relay.- 5. is short-circuited, and. the upper andlowerwindings thereof are energized in cumulae tive; relation; causing, the signal relay R315: to. operate;

Upon operating the signal relay R375 intere rupts, at the contacts all, the path for short, circuiting the upper winding of the supervisory rela Rfifill and, the multiple. circuit for, energizing thcwlower inding of the supervisory relay R358 inserieswith the winding of the front supervisory.- relay- Rfifitlf. Also the; signal relay R3} corn.-v

pletes;,- at the :contacts .Iifiii, .a. circuit for. energizins he'winding. of he control relay Res in series-withthe upper winding of the supervisory relay-Rims; and a multiple path iorshort-circuitingithe. winding of the control. relay R345, the

lower windinemithesupervisory relay Rssaand.

the; windingof the front, supervisory relay. R2585 inseriescircuit:relation. Atthis timethecontrol; relay.- Rtlili; operates and the supervisoryv relay Eligtiil'is retained in; its operated;- positlom; how eyerthe; front supervisory relay 325W restores. Thfif-OfQGl-"fififlllfli th control relay .iswithout particular effect at this time sincethe seize,- relay, Rtllaioccupies its operated position. HOWreyer, upon restoring the front supervisory relay interrupts; atthecontacts. 25!, the circuit. for,- illuminating the. front. supervisory lamp.

5256, thereby toindioate-to the operator at the oallingswitchboard 2| ii that the-subscriber at the called, subscriber substation Tiitl has answered the: call. Also Whenthetoll connector Elmira sponds to the answering of the vcallat the, called, subscribersubstationTelll the projection of ringreturn ofiringebacktone current. over the. con.-

.nection are interrupted. Accordingly, at this.

time an, established. connection is completed between the calling=:-switchboard 2i ii and the. called subscriber substation 116M; whereby the opera tor at" the calling switchboard Zia may converse Kale and thatallr key K264. extending the cone:- nectionyia the. cord circuitfi l 6.. fllfidrEXClilQl-llg the headset 253,-? from the.establishedconnection.

At the-conclusionofithe, established connection, I

when thesubscriber. atthe; called subscriber substation; Ti'iilt disconnects-, the toll, connector 603 operates in. order to return the; polarity of; the; loop circuit, including the: lineiconductors Cfillfi.

and-Chill. of the trunk 6.05;,whereby the lower winding of the local answer, relay R565. is poled torestora, Upon. restorin the. local answer res.

lay Riiiihinterrupts, at. the @contactsififid; the path;

for applying battery potential via; the lower. winde ingofthegtransfer relay R640. to; the junction be:

tween. the upper andlower windings of the pulse.

19 relay R635; and recompletes, at the contacts 661, the path for connecting ground potential to the junction between the upper and lower windings of the pulse relay R635. At this time the upper winding of the pulse relay R63!) is short-circuited and the lower winding thereof is energized in series with the lower winding of the supervisory relay R450; whereby the pulse relay R630 is retained in its operated position and the supervisory relay R458 restores as it is of the differential type, and the upper winding thereof is energized in series with the winding of the control relay R445. Accordingly, the control relay R445 is retained in its operated position; and upon restoring the supervisory relay R450 interrupts, at the contacts 452, the path for applying battery potential to the junction between the upper and lower windings of the signal relay R415; and recompletes, at the contacts 45!, the path for applying ground potential to the junction between the upper and lower windings of the signal relay R415. Accordingly, the upper winding of the signal relay R415 is short-circuited and the intermediate winding thereof is energized in opposition to the lower winding thereof but predominates thereover so that thesignal relay R415 is retained in its operated position. The intermediate winding of the signal relay R315 is energized in opposition to the cumulative energization of the upper and lower windings thereof; whereby the signal relay R315 restores. Upon restoring the signal relay R315 interrupts, at the contacts 315, the circuit for energizing the winding of the control relay R345 in series with the upper winding of the supervisory relay R350; whereby the control relay R345 restores. Also the signal relay R315 completes, at the contacts 311, the path for short-circuiting the upper winding of the supervisory relay R355 and the circuit for energizing the lower wmding of the supervisory relay R355 in series with the winding of the front supervisory relay R2513. Accordingly, the supervisory relay R350 is retained in its operated position and the front supervisory relay R259 operates. Upon operating the front supervisory relay R255 completes, at the contacts 251, the circuit for illuminating the front supervisory lamp L266 in order to indicate to the operator at the calling switchboard 216 that the subscriber at the called subscriber substation T501 has disconnected.

The operator at the calling switchboard 210 then withdraws the front plug P212 of the cord circuit 210' from the jack J 226 terminating the incoming trunk 220, thereby to interrupt the circuit for energizing the winding of the front supervisory relay R250 in series with the lower winding of the supervisory relay R355 causing the relays mentioned to restore. Upon restoring the front supervisory relay R250 interrupts, at the contacts 25I, the circuit for illuminating the front supervisory lamp L266. Also when the front plug P2l2' is withdrawn from the jack J226 the contacts of the jack JZZU are opened to interrupt the'circuit for illuminating the busy lamp L229 in order to indicate the idle condition of the incoming trunk 220 and consequently the tacts 242 and 255 and the set of switch springs S281, for operating the release magnet M218.

20 Upon operating the release magnet M213 releases the wiper carriage of the Strowger mechanism causing it to be returned to its normal rotary and vertical positions; whereby the sets of switch springs S219, S285 and S28! are operated. More particularly, the set of switch springs S281 is operated in order to interrupt the circuit for operating the release magnet M218; and the set of switch springs S219 is operated in order to complete the previously traced path for applying battery potential by way of the upper winding of the transfer relay R266 to the control conductor C223 of the incoming trunk 220 in order again to mark the incoming trunk 225 and consequently the selector 260 as idle.

Upon restoring the supervisory relay R359 in the repeater 300 interrupts, at the contacts 352, the path for applying battery potential to the junction between the upper and lower windings of the signal relay R315; and completes, at the contacts 351, the path for applying ground potential to the junction between the upper and lower windings of the signal relay R315. Accordingly, at this time the upper winding of the signal relay R315 is short-circuited and the intermediate winding of the signal relay R315 is short-circuited in series with the intermediate winding of the signal relay R415; whereby the signal relay R315 is retained in its restored position. Since the upper winding of the signal relay R415 is short-circuited and the intermediate winding thereof is now short-circulted, the latter relay restores. Upon restoring the signal relay R415 interrupts, at the contacts 416, the circuit for energizing the winding of the control relay R445 in series with the upper winding of the supervisory relay R456; whereby the control relay R445 restores. Also the signal relay R415 coinpletes, at the contacts 411, the path for shortcircuiting the upper winding of the supervisory relay R456 and the multiple path for short-circuiting the lower winding of the supervisory relay R456 in series with the lower winding of the pulse relay R630, thereby to retain the supervisory relay R456 in its restored position and to cause the pulse relay R635 to restore. Upon restoring the control relay R445 interrupts, at the contacts 446, the circuit for retaining operated the busy relay R435 in order to cause the latter relay to restore shortly thereafter, it being of the slow-torelease type. Upon restoring the busy relay R436 interrupts, at the contacts 433, the path for applying ground potential to the control conductor C413 of the incoming trunk 4H); and completes, at the contacts 43], the path for applying battery potential by way of the upper winding of the seize relay R446 to the control conductor C413; thereby again to mark the incoming trunk 410 and consequently the repeater 4110 as idle to the selectors 521, etc., having access thereto. Also the busy relay R435 interrupts, at the contacts 434, the path for applying ground potential to the control conductor C423 of the outgoing trunk 42!] in order to interrupt the holding circuit for energizing the intermediate winding of the test relay R536 causing the latter relay to restore. Upon restoring the test relay R536 completes, at the contacts 535, a circuit, including the contacts 542 and 555 and the set of switch springs S58I, for operating the release magnet M518. Upon operating the release magnet M518 releases the wiper carriage of the Strowger mechanism causing it to be returned to its normal rotary and vertical positions; whereby the sets of switch springs S519, S539 and S58! areoperated.

More particularly, the set of SWltCIYSDIiHgS'S5BI is operated in order to interrupt the circuit for operating the release magnet M518; and the set. ofswitch springs S5 19 is operated in order again toapply battery potential by way of the upper Winding of the transfer relay R560 to the control conductor C423 of the outgoing trunk 420.

When the incoming selector 506 is thus .released, ground potential is removed therein from the control conductor C613 of the incoming trunk 6H]; and when the pulse relay R630 restores, it interrupts, at the contacts 63!, the circuit for retaining operated the hold relay R535 in order to cause the latter relay to restore shortly thereafter, it being of the slow-to-release type. Upon restoring the holdrelay R635 interrupts, at the contacts 636, the multiple path for applying ground potential to the control conductor'C6l3 of the incoming trunk Ellhthereby to interrupt the holding circuit for energizing the intermediatewinding of the testrelay R620 causing the latter relay to restore. Upon restoring thehold relay R635 completes, at the contacts 535, a circult, including the contacts 632 and the set of switch springs S698, for operating the release magnet M681 Upon operating the release magnet M68'! releases the wiper carriage of the Strowger mechanism causing it to be returned to itsnormal rotary and vertical positions; whereby the sets of switch springs S688, S689, S690 and S693 are operated. More particularly, the set of switch springs S696 is operated in order to interrupt the circuit for operating the release magnet M687; and the set of switch springs S688 is operated in order to complete the path for applyingbattery potential by way of the upper winding of the transfer relay R649 to the control conductor C613 of the incoming trunk 6H3, therebyagain to mark the incoming trunk6l0 and con sequently the toll selector repeater 600 as idle to the incoming selectors 566, etc., having access thereto. Also when ground potential is removed from the control conductor C6I3 of the incomingtrunk 5H1, the holding circuit for energizing the local relay R645 is interrupted causing the latter relay to restore, and the circuit for energizing the upper winding of the local answer'relay R665 is interrupted in order to retain the latter relay in its restored position. When the toll selector repeater 600 is thus released, ground potential is removed from the control conductor C668 of the trunk 605 in order to effect the release of the toll connector 6&3; whereby battery potential in the toll connector 6433 applied to the control con ductor C668 of the trunk 605 again marks thetrunk 665 and consequently the toll connector 603 as idle to the toll selector repeaters 600, etc., having access thereto. Also when the toll connector 603 is thus released, the line switch associated with the subscriber line 662 again operates in order to mark the called subscriber substation T601 as'idle. At this time the established con-.- nection between the calling switchboard 2H) and the called subscriber substation Tfilll is released and all of the apparatus involved therein is completely released and available for further'use;

Reconsidering the extension of the call from. the calling switchboard m to the called subscriber substation Tel-H, the selector 260 may re spond to the first digit of the directory number" oithe called subscriber substation Tfilll and. test allof the incoming trunks in the group,including1* the incoming trunk 386, as busy. In thiscaseoperation of the rotary magnet M2'I6'continues:;;, whereby the wiper carriage of the Strowgen mechanism is driven eleven steps: in the -rotar it direction"awayfrom its normal rotary position" operating the sets of switch springs'S282, S283 Upon operating the set of switch. springs S282 completes acircuit, including-the grounded control conductor C223 of the incoming trunk 220 for energizing the upper winding ofthe test relayRZBElin series with the upper winding of the transfer relay R260, thereby to effect opera-- tion of the relays -mentioned. Upon operating thetest relay R236 interrupts, at the contacts 235; the circuit for-operating the rotary magnet M216 in order to arrest further operation thereof and-the multiple circuit for retaining operated the hold relay R250; in order to cause the latter relayto restore shortly thereafter, it being of the slow-to-release type. R230 interrupts, at the contacts 234, the circuit for'retaining operated the pulse relay R240; and

completes, at the contacts 233, a connection'be tween the EC'conductor C224 of the incoming trunk 220 and the EC wiper 214. When the set ofswitch springs S284 is thus operated, the toll busy conductor C285 is connected to the winding ofthe busy relay R265; and 120 ground impulses per minute appearing upon the toll busy con-- diictor C285 cause corresponding operation and restoration of the busy relay R265; Each time the-busy relay R265 operates, it interrupts, at the contacts 256; apath, including the set of switch springs S283, for applying ground potential to the controlwiper 214; and completes, at the con tacts 262 a path, including the setof switch.

springs S263, for applying resistance battery por tentialto the control wiper 2M. Conversely, each time the busy relay R265'restores, it opens the contacts 2El and closes the contacts 266; whereby minute indicates to the operator at the calling switchboard 2|!) that a toll busy condition has been encountered in the outgoing switch train by'the selector 266." Theoperator at the calling switchboard 2H3 then withdraws the front plug P2l2 from'the jack J22Ei effecting the release ofvthe selector 2st in a manner. substantially identicalto that previously explained. When thewiper carriage of the Strowger mechanism is thus released, the sets of switch springs S2l9, $280,.

$26!, S282, S283 and S284 are operated. At this time the set of switch springs $28G is operated in order to effect the restoration of the busy relay R265;- and the set of switch springs S283 is op erated in' order to disconnect groundpotential' fromthe EC wiperZM;

Ina similar manner the incoming selector 500 may respond to the second digit of the directorynumber of the called subscriber substation TEBI and test all of thetrunks in. the group, include. ingthe incoming trunk Bill, as busy; case, the wiper carriage of the Strowger mecha--.

nism is driven eleven steps in the rotary direc-- tion away from its normal rotary position efiect-- ing operation of the sets of switch springs S582,

S583and S584 and the consequent intermittent operation of theubusy relay R565; wherebythe Also the test relay The flashing of the front supervisory lamp L266 at 120 times per In this;

23 encountered by the incoming selector 566. At this time the operator at the calling switchboard 2l6 withdraws the front plug P212 from the jack .1226 efiecting the release of the apparatus involved in a manner substantially identical to that previously explained.

In a similar manner the toll selector repeater 666 may respond to the third digit of the directory number of the called subscriber substation T661 and test all of the trunks in the group, including the trunk 665, as busy. In this case the wiper carriage of the Strowger mechanism is driven eleven steps in the rotary direction away from its normal rotary position effecting operation of the sets of switch springs S661 and More particularly, the set of switch springs S692 is operated to complete a circuit, including the grounded control conductor C613 of the incoming trunk 636, for energizing the upper winding of the transfer relay R646 in series with the upper winding of the test relay R626; whereby the relays mentioned operate. Upon operating the test relay R620 interrupts, at the contacts 62l, the circuit for operating the rotary magnet M666. The set of switch springs S691 is operated to complete a connection between the upper winding of the toll answer relay R666 and the toll busy conductor C616 and a multiple connection, also including the contacts 652, between the winding of the toll relay R656 and the toll busy conductor 0676. Since 120 ground impulses per minute are applied to the toll busy conductor C616, the winding of the toll relay R666 is energized upon the first application of ground potential upon the toll busy conductor C6'l6 causing the latter relay to operate and complete, at the contacts 651, a holding circuit, including the grounded control conductor CNS of the incoming trunk 616, for energizing the winding thereof. Also upon operating the toll relay H666 interrupts, at the contacts 652, the connection between the winding thereof and the toll busy conductor C616. The upper winding of the toll answer relay R666 is intermittently energized via the toll busy conductor C616 operating and then restoring in a similar manner. Each time the toll answer relay R666 operates, it interrupts, at the contacts 661, a path, including the contacts 623 and 653, for applying battery potential by way of the lower winding of the transfer relay R6416 to the junction between the upper and lower windings of the pulse relay R636; and completes, at the contacts 662, a path, including the contacts 653, for applying ground potential to the junction between the upper and lower windings of the pulse relay R636. Conversely, each time the toll answer relay R666 restores, it opens the contacts 662 and closes the contacts 661; whereby 126 ground and battery impulses per minute are returned over the EC conductor C616 of the incoming trunk 6E6 causing the front supervisory lamp L266 to be flashed a corresponding manner indicating the toll busy condition encountered by the toll selector repeater 666. The operator at the calling switchboard 266 then withdraws the front plug P252 from the jack J226 effecting the release of the apparatus involved in a manner substantially identical to that previously explained.

Finally, the toll connector 663 may respond to the fifth digit of the directory number of the called subscriber substation T661 and test the subscriber line 662 extending to the called subscriber substation T661 as busy; whereby the toll connector 663 operates to reverse and re store the polarity of the loop circuit, including the line conductors C666 and C661 of the trunk 665, sixty times per minute; whereby the local answer relay R665 follows, repeating, at the contacts 66! and 666 corresponding ground and battery impulses over the EC conductor C614 in order to bring about corresponding flashing of the front supervisory lamp L266. Flashing of the front supervisory lamp L266 at sixty times per minute indicates to the operator at the calling switchboard M6, the line busy condition encountered by the toll connector 663. The operator at the calling switchboard 216 then withdraws the front plug P252 from the jack J226 efiecting the release of the apparatus involved in a manner substantially identical to that previously explained.

In view of the foregoing it will be understood that a call may be extended from the calling switchboard 516 in the office 26 to a called subscriber substation, such for example, as the called subscriber substation T261 in the office 16 in a substantially identical manner. Specifically, this call may be routed from the calling switchboard 516 via the incoming trunk 526, the selector 521, the incoming trunk 416, the repeater 466, the trunk 396, the repeater 366, the outgoing trunk 326, the incoming selector 265, the incoming trunk 266, the toll selector repeater 264, the trunk 21 l, the toll connector 263 and the subscriber line 262 to the called subscriber substation T261.

Now assuming that a call is to be extended from the calling switchboard 216 in the office 16 to the called switchboard 516 in the office 26, the connection may first be routed from the calling switchboard 216 via the incoming trunk 226, the selector 266, the incoming trunk 316, the repeater 366, the trunk 396, the repeater 466, the outgoing trunk 426, the incoming selector 566 and the incoming trunk 616 to the toll selector repeater 666 in respons to inserting the front plug P212 of the cord circuit 216 into the jack J226 and the subsequent dialing of the first two digits of the directory number of the calling switchboard 516. The operator at the calling switchboard 216 then proceeds to dial the third digit of the directory number of the called switchboard 516; whereby the toll selector repeater 666 responds thereto in a manner substantially identical to that previously explained selecting first the group of trunks, including the trunk (H5, and then an idle trunk in the group mentioned. Specifically, the wiper set of the toll selector repeater 666 may select the particular trunk 615 extending to the ringdown trunk circuit 666; whereupon the test relay R626 is operated in the manner previously explained. At this time the set of switch springs S693 is not operated since the wiper carriage of the Strowger mechanism has been driven in the vertical direction to the level in which the group of trunks, including the trunk 615, is terminated and indicating a toll call. Accordingly, when the test relay R626 operates, ground potential is applied via the contacts 621 and 642 and the control wiper 683 to the control conductor C616 of the trunk 6E5 effecting seizure of the ring-down trunk circuit 568. Also at this time, the previously traced path for bridging the lower winding of the local answer relay R665 across the line wipers 681 and 682 and consequently across the line conductors C616 and C617 of the trunk 615 is completed. Ground and battery amazes potentials in tharing-down trunk circuit 504 are. applied to. the line conductors Cliit'and C611 of the trunk- 515 of the predetermined polarity; whereby the lower winding of the local answer relay R655 is poled to; operate. Upon operating the local answer relay R555 completes, at the contacts 556, a circuit, including the first contacts" of the set of switch springs St-ildfor operating the toll relay R850. Upon operating the toll relay Refit completes, at the contacts 55!, a holding circuit, including the grounded control conductor C513 of the incoming trunk Bid, for energizing the winding thereof; and. interrupts, at the contacts 551, the loop circuit for energiz ing the lower winding of the answer relay R505 causing the latter relay to restore. Also the toll relay R550 completes, at the, contacts 556, a path, including the. windings 528, 529 of the repeating coil 525, the contacts the contacts 51!, 5.14 and the line wipers 55:5, 682 for bridging the lower winding of the. toll answer relay R555 across the line conductors CH5 and. can of the trunkltl 5. The lower: winding of the toll answer relay R553.- is energized via the loop circuit including the. line. conductors. C595 and C551 of the trunk 515 extending to the ring-down trunk circuit 55% causing the. latter relay to operate. Upon operating the toll answer relay R560 completes, at the contactsfithan alternative path, including the contacts-553, for applying ground potential to the junction between the upper and lower windings of the pulse relay R555, thereby to retain operatedithepulse relay R550 and to retain restored the supervisory relay R4553. Accordingly, the signal relay- 3.515 is retained in its restored position retaining the; supervisory relay R350 and the front supervisory relay R250; in their operated positions; whereby thefront super:- visory lamp L255 is. illuminated indicating to the operator at. the calling switchboard 2 l-that thecall has not yet been answered-.- While the application of ground potential to the control conductor (352-5 of the trunk 13 l 5 marks the trunk 6i5 as busy to the other toll selector repeaters having access thereto and-:efiects seizure of the ring-down trunk circuit 553, no signal is actually transmitted from the ring-down trunk circuit 503* over the trunlr 555 to. thecalled switchboard 519 at this time.

When the operator. at the calling switchboard are is ready to signal the operator at the called switchboard Elli, she operates and then restores the front; lie-y. K2552 When the ring front key isthus operated, there is completed, at the'fn'st contacts thereof, a circuit for operate ing the ring relay R255; and when the ring key K2555" is thus restored, the circuit for retaining operated. the; ring relay R230" is interrupted causing the latter r lay to restore shortly thereafter, it being of the slow-to-release type. Also whenthe ringkey K255 is thus restored, there is completed, at the second contacts thereof, a circuit, including the contacts 251' for operating the ring. relay R220 Upon restoring the ring relay R250 interrupts, at the contacts 25!, the circuit for retaining operated the ring relay Accordingly, the ring relay R220 operates and then restores completing, and then interrupting, at the contacts 22-l' and 222, paths for applying battery potential by way of the re.- sistors 213" and 2:15! to the tipv and the ring of .16 front plug Pi3l2 and consequently to the line conductors C225. and C222of the incomin trunk 220 and; the line. conductors Ci il and C3l2 of the incoming, trunk 310.; whereby the. ring, control. relays R355 and R360 in the repeater 300 operate and'then restore. Upon operating and then restoring th ring control relay R360 completes and then interrupts, at the contacts 36L a circuit for energizing the winding of the control relay R355 in series with the upper winding of the supervisory relay R350 and a multiple path for short-circuiting the winding of the control relay R345. in series with thelower winding of the supervisory relay R350 and the winding of the frontsupervisory relay R250; whereby the supervisory relay R350 is' retained in its operated positionand the control relay R345 opcrates and then restores while the front supervisory relay R255. restores and then reoperates. The operation and subsequent restoration of the controlrelay Rfi itis without effect, whereas the restoration and subsequent reoperation of the front supervisory relay R250 effects a flash of the front supervisory lamp L266" indicating that the repeater 300 is responding to the ring control.

When the ring control relay R355 operates and then restores, it completes and then interrupts, at the contacts 355, a circuit for operating the control relay R355; whereby the control relay R35'5 operates and then restoresshortly thereafter, it being of the slow-to-release type. Upon restoring the ring control relay R355 completes, at the contacts 351, a circuit, including the contacts 355, for operating the control relay R310; and upon restoring thecontrol relay R355 interrupts, at thecontacts 365, the circuit for retaining operated the control relay R310. Accordingly, the control relay R310 operates and then restores. When the control relay R310. operates, it interrupts, at the contacts 312, the path for applying battery potential to the junction. between the upper and lower windings of the signal relay R315; and completes, at the contacts 31 I, a. path for applying ground potential. to the junction between the upper and lower windings of the signal relay R315. Conversely, when the control relay R310 restores, it opens the contacts 31! and closes the contacts 312. Accordingly, an impulse of ground potential is transmitted over the trunk 3510 causing the. signal relay R415 in the repeater 400. to restore and then reoperate'. When theysignal relay R415 restores and then reoperates, it interrupts and then recompletes, at the contacts. 415, the circuit for energizing the windingof the control relay R445 in series with the lower winding of the supervisory relay R450 and. the lower winding of the pulse relay R555; and completes, and then interrupts, at the contacts 411, the path for shortcircuiting the lower winding of' the supervisory relay R450? in series with the, lower winding of the pulse relay R535. Accordingly, the supervisory relay R l50-iis retained in its restored position and the control relay R445 and the pulse relay R3llirestore and then reoperate. The restoration and subsequent reoperation of the control relay R545 is without particular effect since the. busy rleay Rdtllxis of the slow-to-release type; However. upon restoring and then reoperating therpulse relay R530 completes and then interrupts, at the; contacts 632, the circuit for energizing" the lower winding; of the transfer relay R545 in order, to cause-thelatter relay to operate and remain-operated a short time. interval as it is of the slow-to-release type. Upon operating the transfer relay R540 completes, at: the contacts. 543, a circuit, including the contacts 655 for energizin the lower winding. thereof in series with the winding of the ring relay R615; thereby to effect operation of the ring relay R610 and further to delay the restoration of the transfer relay R646. The winding of the ring relay R616 is of suiiicie'nt high resistance that the lower winding of the transfer relay R640 is not locked in series therewith; rather the transfer relay R640 restores after a time interval interrupting, at the contacts 643, the circuit for energizing the lower winding thereof in series with the winding of the ring relay R610. Accordingly, the ring relay R610 is retained in its operated position for a predetermined time interval and then restores. Upon operating the ring relay R610 interrupts, at the contacts 61] and 614, the previously traced circuit for bridging the lower winding of the toll answer relay R660 across the line conductors C6l6 and C611 of the trunk 615; and

\ completes, at the contacts 612 and 613, connections between the generator conductor C615 and ground potential and the respective line wipers EM and 682; When the ring relay R610 restores, it interrupts, at the contacts 612 and 613, the circuit for projecting ringing current over the line conductors C6l6 and C641 of the trunk 615; and recompletes, at the contacts 615 and 614, the previously mentioned path for bridging the lower winding of the toll answer relay R660 across the, line conductors C6l6 and C6l1. Accordingly, ringing current is projected over the line conductors C6|6 and C611 of the trunk 6E5 for the predetermined time interval mentioned ringing down the ring-down trunk circuit 508; whereby the ring-down trunk circuit 563 transmits a signal over the trunk 509 indicating to the operator at the called operator position 550 that a call is waiting to be answered on the trunk 509.

The operator at the called switchboard 510 answers the call by inserting the rear plug of a cord circuit thereat into the jack terminating the trunk 506; whereby the ring-down trunk circuit 508 is controlled tointerrupt the loop circuit extending via the line conductors C616 and CH1 of the trunk M for energizing the lower winding of the toll answer relay R660 causing the latter relay to restore. Upon restoring the toll answer relay R660 interrupts, at the contacts 662, the path for applying ground potential to the junction between the upper and lower Windings of the pulse relay R630; and completes, at the contacts 56!, the path for applying battery potential by way of the lower winding of the transfer relay R640 to the junction between the upper and lower windings of the pulse relay R630; whereby the pulse relay R660 is retained in its operated position and the supervisory relay R450 is operated. Upon operating the supervisory relay R450 effects operation of the signal relay R315 and the consequent operation of the control relay R345 and the restoration of the front supervisory relay R250. Upon restoring the front supervisory relay R250 extinguishes the front supervisory lamp L266 indicating to the operator at the calling switchboard 2l0 that the operator at the called switchboard 516 answered the call. At this time, an established connection is completed between the calling switchboard 2m and the called switchboard 580 and the operator at the called switchboard 5H3 is advised concerning the further extension of the connection.

At the conclusion of the established connection when the operator at the called switchboard 5l0 withdraws the rear plug of the cord circuit thereat from the jack terminating the trunk 506-, the ring-down trunk circuit 508 is controlled to recomplete the loop circuit including the line conductors C6I6 and CH1 of the trunk M5 for energizing the lower winding of the toll answer relay R660 causing the latter relay to operate Upon operating the toll answer relay R660 interrupts, at the contacts 66I, the path for applying battery potential by way of the lower winding of the transfer relay R640 to the junction between the upper and lower windings of the pulse relay R630; and completes, at the contacts 662, the path for applying ground potential to the junction between the upper and lower windings of the pulse relay R630; whereby the pulse relay R630 is retained in its operated position and the supervisory relay R450 is restored. Upon restoring the supervisory relay R450 effects the restoration of the signal relay R315 and the consequent restoration of the control relay R345 and reoperation of the front supervisory relay R250. Upon reoperating the front supervisory relay R250 again illuminates the front supervisory lamp L266 in order to indicate to the operator at the calling switchboard 2l0 that the operator at the called switchboard 5l0 has disconnected.

The operator at the calling switchboard 2l0 then withdraws the front plug P212 from the jack J220 in order to effect the release of the selector 200, the repeaters 300 and 400, the incoming selector 500 and the toll selector repeater 600 in a manner substantially identical to that previously explained. When the toll selector repeater 600 is thus released, ground potential is removed from the control conductor C6l8 of the trunk 6i 5; whereby battery potential in the ringdown trunk circuit 508 is again applied to the control conductor C6I8 marking the trunk 6E5 and consequently the ring-down trunk circuit 508 as idle to the toll selector repeaters 600, etc., having access thereto. At this time the established connection between the calling switchboard 2I0 and the called switchboard 5"] is released and all of the apparatus involved therein is completely released and available for further use.

In view of the foregoing, it will be understood that a call may be extended from the calling switchboard 5|0 in the oflice 20 to the called switchboard 2l0 in the oflice l0 in a substantially identical manner. Specifically, this call may be routed from the calling switchboard 5l0 via the incoming trunk 520, the selector 52!, the incoming trunk M6, the repeater 400, the trunk 390, the repeater 300, the outgoing trunk 320, the incoming selector 205, the incoming trunk 206, the toll selector repeater 204, the trunk 201, the ring-down trunk circuit 208 and the trunk 209 to the terminating jack J 209 at the called switchboard 2I0.

Considering now in greater detail the operations of the signal relays R315 and R415 in the repeaters 300 and 400 respectively disposed in the ofiices l0 and 20 respectively and interconnected by the trunk 360 via the simplex conductors C385 and C485, it will be recalled that the circuits for energizing the upper windings of the signal relays R315 and R415 are respectively locally controlled from the exchange batteries respectively disposed in the oiiices I0 and 20, while the circuits for selectively energizing and shortcircuiting the intermediate windings of the signal relays R315 and R415 are under the joint control of the exchange batteries in the offices l0 and 20, and the circuits for energizing the lower 

